Soetener for synthetic rubber



Patented May 18, 1943 sor'rannn FOR SYNTHETIC RUBBER Doran E. Sauser, Cuyahoga Falls, Ohio, assignor to The B. F.

Goodrich Company, New York,

N. Y., a corporation of New York No Drawing. Application June 2 1942, Serial No. 445,481

. 5' Claims.

This invention relates to a new class of softeners for synthetic rubberand to improved compositions obtainable by the use of such softeners.

It is well known that butadienes' may be polymerized either alone or in the presence of other unsaturated compounds copolymerizable therewith to form polymers resembling natural rubber. It has been found that in order to employ these synthetic rubbers, softeners or plas-- ticizers must be incorporated therein, usually in larger amounts than are ordinarily used innatural rubber compositions. The softening of synthetic rubber has in general presented problems not encountered in the softening of natural rubber due to different behavior on mill rolls, incompatibilityof synthetic rubber with certain softening and plasticizing materials commonly employed in natural rubber, and other differences in properties. 'It has been particularly difficult to find satisfactory softeners'for the oil-resisting synthetic rubbers such as copolymers of butadiene and acrylonitrile and plastic polymers of chloroprene, for many softeners are oily materials of the types which these synthetic rubbers resist. I

It is the principalobject of this invention to provide a new class of softeners which may be employedrwith-synthetic rubbersprepared by the polymerization of butadienes-l,3, and particularly those prepared by the copelymerization of 2 butadiene and acrylonitrile. It is a further objectof this invention to provide softeners which-- aid in the incorporation of compound ingredients on a roll mill and which aid in the production of vulcanizates having a low durometer hardness,

high rebound elasticity, low temperature flexibility and a good tensile strength.

These and other objects are effected by incorpbrating an aliphatic nitrile containing an open' chain of at least ten carbon atoms in a synthetic rubber produced by the polymerization ofa butadiene-L3. As examples of suitable softeners may be mentioned dodecane nitrile, tetradecane .nitrile, hexadecane nitrile, octadecane nitrile, 9- octadecene nitrile,'.etc. These nitriles are conammonla and 'dehydrating the products. Since individual fatty "acids are relatively diflicult to obtain in the pure state, it 'is ordinarily expedient to employ nitriles prepared from mixtures of bers prepared by the polymerization of a blltfln veniently prepared by treating fatty acids with dime-1,3, 'by which is meant butadiene-1,3 and its homologues and analogues which polymerize in essentially the same manner such as isoprene, 2,3-dimethylbutadiene, piperylene, chloroprene, etc., either alone or in admixture with each other and/ or mono-olefinic monomers cop'olymerizable therewith such as styrene, vinyl naphthalene, isobutene, acrylonitrile, alphamethacrylonitrile, alpha chloroacrylonitrile, methyl methacrylate, methyl acrylate, alphachloro methyl acrylate, vinylidene chloride, methyl isopropenyl ketone, methyl vinyl ether, and other mono-oleflnic hydrocarbons, esters, ethers, and ketones. The copolymerization to form a synthetic rubber may be accomplished by any of the well-lmwn methods such as homogeneous polymerization, polymerization in aqueous emulsion, etc.

The softeners of this invention may be incorporated into the synthetic rubber by any desired method as by adding the softener to the monomer prior to or during the polymerization, adding the softener while the synthetic rubber is being worked on a roll miIL'masticating a mixture of synthetic rubber and the softener in an internal mixer, or adding the softener to a solution or dispersion of the synthetic rubber.

The amount of softener added will depend upon the properties desired in the softened composition and upon the nature of the synthetic rubber treated. The higher aliphatic nitrlles are compatible. with even the oil-resisting synthetic rubbers such as copolymers of butadiene and acrylonitrile over a wide range of proportions. Compositions containing an' equal amount by weight of softeners and synthetic rubber may be employed, although between and parts and not more than about parts by weight of softeners for each 100 parts of synthetic rubber are generally'employed in the manufacture of tires, inner tubes, hose,'belts, and similar rubber goods in which the softener is employedmainly to assist in compounding and processing operations rather than to vary the properties of the vulcanizates.

As an example of the use of one of the softeners of this invention, 50 parts by weight of .9 octadecene nitrile, were emp ye as a softener in a composition containing 100 parts by weight of a synthetic rubber prepared by the emulsion copolymerization of parts by weightof butadiene and 45 parts of acrylonitrile, and other ordinary compounding ingredients such as gas black, antioxidant, accelerator, and softeners. The compounded stock had a plasticity of .0.5 as measured by a Dietrich-Karrer plastometer employing a 10 lb. weight at 35 C. A similar composi tion in which dibutyl phthalate, one of the best and most widely used softeners for this type of synthetic rubber, was employed instead of the 9-octadecene nitrile exhibited a plasticity of only 15.3 under the same conditions. Furthermore, the vulcanizates prepared from the composition softened with 9-octadecene nitrile exhibited an unusually high tensile strength for such a soft synthetic rubber. Excellent softening action is also exhibited by other higher aliphatic nitriles and scope of the invention as defined in the appended claims.

I claim: 1. A composition of matter comprising a synthetic rubber prepared by the polymerization of a butadiene-1,3, and, as a-softener therefor, an aliphatic nitrile containing an open chain of at least ten carbon atoms.

'2. A composition of matter comprising a copolymer of butadiene-1,3 and a copolymerizable mono-olefinic compound and, as a softener therefor, an aliphatic nitrile containing an open chain of at least ten carbon atoms.

3. A composition of matter comprising a copolymer of butadiene-l,3 and acrylonitrile and, as a softener therefor, an aliphatic nitrile containingan open chain of at least ten carbon 'atoms.

4. A composition of matter comprising a syn-- thetic rubber prepared by the polymerization of a butadiene-1,3, and, as a softener therefor, 9-

octadecene nitrile.-

5. A composition of matter comprising a copolymer of butadiene- ,3 and acrylonitrile and, as a softener therefor, 9-octadecene nitrile;

DORAN E. SAUSER.

DISC'L'AIMER- 2,319,634;Doran E. Sauser, Cuyaho'g'a, Falls, Ohio. SOFTENER FOR fSYN'nfiE'ric RUBBER. Patent dated May 18, .1943; Disclaimer .filgd October 25, 1944, by the assignee, The B. F. Goodr'ih Company. I Hereby ent ersfthis disclaimer to claim .5 fjsaid patenth -[0 flicial Gazette November 21, 1944.] Q 

